[PATCH] D72643: [InstCombine] form copysign from select of FP constants (PR44153)

[Nikita Kniazev via Phabricator via llvm-commits]

nick added a comment.

I cannot be a reviewer, just added some dummies questions. And, @spatel, thanks for working on this!



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Comment at: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp:2331
+  if (!match(TVal, m_APFloat(TC)) || !match(FVal, m_APFloat(FC)) ||
+      !abs(*TC).bitwiseIsEqual(abs(*FC)) || TC == FC)
+    return nullptr;
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I would never expect `TC == FC` to happen here. Are branches folded later than this transform?


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp:2338
+  ICmpInst::Predicate Pred;
+  if (!match(Cond, m_OneUse(m_ICmp(Pred, m_BitCast(m_Value(X)), m_APInt(C)))) ||
+      !isSignBitCheck(Pred, *C, IsTrueIfSignSet) || X->getType() != SelType)
----------------
Is the one use check necessary? I would imagine that this transform will unblock other one use transforms.


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